A device is known from EP 511 050 A1, which includes at least one aerodynamically shaped element, at least one part or one zone of which is able to fold up, for the purpose of propulsion and/or lift under the effect of the wind directed thereon, having two surfaces, one for the pressure (windward) side and one for the suction (leeward) side, in which at least one slit is provided to permit the flow of air from the pressure side to the suction side, and control elements are provided to conduct the air exiting the aforementioned slit on the suction side tangentially to the aforementioned element, in which the aforementioned slit and the aforementioned control elements of the aforementioned flow have an effect on the position and on the geometry of at least one part and/or one zone of the aforementioned element with regard to the geometry and the opening/closure with the aid of devices, and in which the aforementioned device furthermore includes means which control the geometry of the aforementioned element, at least the shape and depth of the concavity, for the purpose of providing an aerodynamic element having an adjustable geometry, which is equipped with means which improve the air flow from the pressure side to the suction side in such a way that the air on the suction side empties into a flow which flows in the same direction and on the same side as the flow of the suction-side outflow at the junction between the aforementioned flow and the aforementioned outflow, the element retaining its aerodynamic shape. (i.e., without shifting, without concavity, without an obstacle which forms a conducting element, among other things), even if no air through-flow arises (for example if the aerodynamic element is only slightly curved and if a principle is used which is valid for all elements of an aerodynamic shape for the thin as well as for the thick hydrofoils).